Photographic gelatin-silver halide emulsions containing beta-hydroxyalkyl ethers of polyvinyl alcohol



United States Patent 3,043,698 PHOTOGRAPHIC GELATIN-SILVER HALIDE EMULSIONS CONTAINING p-HYDROXYAL- KYL ETHERS OF POLYVINYL ALCOHOL Vaughan Crandall Chambers, Jr., Fair Haven, N.J., as-

signor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Fiied Aug. 18, 1960, Ser. No. 50,324 1 10 Claims. (Cl. 96-114) This invention relates to photographic gelatino-silve'r halide emulsions and emulsion layers having improved photographic characteristics and to protographic elements, e.g., plates, films and papers embodying the same. The invention also relates to a process for increasing the covering power and improving the maximum density, contrast and effective speed of gelatino-silver halide emulsions.

It is known to add certain chemical compounds, e.g. heavy metal and noble metal salts to improve the sensitometric characteristics of photographic gelatino-silver halide emulsions. There is, however, at the present time, a practical limit to the advantages which can be obtained by the addition of such compounds without accompanying deleterious effects such as uncontrollable fog and instability on tropical aging,

It has been proposed to add to, or replace all or part of the gelatin in a gelatin silver halide system with various polymeric colloid materials for various reasons including attempts to overcome the well-known disadvantages of gelatin. However, none of these proposals have overcome these disadvantages in a completely satisfactory manner, and gelatin is still used in most commercial photographic films. In general, when all of the gelatin is replaced by the synthetic polymers suggested by the prior art, the outstanding photographic and colloid-chemical properties of gelatin are lost. In addition,'it is' difficult to determine the optimum conditions for the addition of coating aids, coating and drying, etc. to form a photographic element possessing satisfactory hardness and stability. This is particularly true when the exposed element contains the usual photographic hardeners and is placed in photographic processing solutions.

The silver halide emulsions of this invention comprise gelatino-silver halide emulsions containing on a dry basis, by weight 30% to 75% silver halide, 20% to 65% gelatin and to 50% of a [:l-hydroxyalkyl ether of a polyvinyl alcohol, wherein the alkyl group contains 2-3 carbon atoms and which are completely and readily soluble in water at room temperature. The three constituents are, of course, so adjusted in amount so that they do not total more than 100% by weight. The amount of the polymen'c binders is based on the weight of the finished silver halide emulsion ready for coating onto a support.

The photographic elements of the invention comprise a support, gelatino-silver halide emulsion layer and in the same layer and/or in a non-light-sensitive separate gelatin layer contiguous therewith 5% to 50%, by weight, based on the total weight of said layers, on a dry basis, of a B-hydroxyalkyl ether of polyvinyl alcohol as described above.

The fi-hydroxyethyl, B-hydroxypropyl and mixed hydroxyethyl/hydroxypropyl polyvinyl ethers contain units represented by the formulae:

3,043,698 Patented July 10, 1962 where R is beta-hydroxyethyl or beta-hydroxypropyl an m and n represent the proportions of such units in the polymer or copolymer and mm is in the ratio of 1:0 to 03:1.

Hydroxyethyl and hydroxyp-ropyl ethers of polyvinyl alcohol can be prepared by the general method of S. E. Cohen, H. C. Haas and H. Slotnick, J. Poly, Sci, 11, 193-201 (1953) and methods of French Pat. 708,236.

By polyvinyl alcohols, as used in preparing the hydroxyalkyl ethers by reaction with an olefin oxide, is, meant the hyd-roxyl polymers containing a large number of recurring intralinear vinyl alcohol (CH CHOH-) units known in the art prepared by polymerizing a vinyl ester, e.g., vinyl acetate, vinyl chloracetate, vinyl propionate, vinyl butyrate, etc., followed by partial or complete hydrolysis and if desired by further reaction to introduce minor portions of other modifying groups, e.g., acetal, ester or ether groups, e.g., acetaldehyde or formaldehyde acetal groups; acetate, chloracetate, propionate or butyrate groups and methoxy or ethoxy groups.

Hydroxyethyl vinyl ether/vinyl alcohol copolymers are preferably prepared, however, by polymerizing hydroxyethyl vinyl ether and vinyl acetate in an alcohol solvent using azobisisobutyronitrile or similar catalyst and then hydrolyzing the resulting copolymer by reaction with basis 5 to 50% of the above described polymeric material, 20 to 65 of gelatin, and 30 to 75 silver halide,

all by weight. The emulsions may, of course, contain small amounts of conventional adjuvants. The final emulsions have markedly increased covering power (e.g.,

'10 to 60% greater) over all gelatin emulsions, which is quite surprising. To be more specific, with respect to covering power for the same quantity of silver halide, large increases in maximum density and contrast can be obtained in the developed image. Covering power can be expressed as the numerical result of dividing optical density by the grams of silver per square decimeter in the developed image layer. The covering power will, of course, vary with the amount of the polymeric material used;

The invention is especially suited to photographic silver halide emulsions for radiological films, particularly those for medical diagnostic-work. However, the invention is by no means limited to any particular type of photo-- graphic emulsion, and the polymeric material may be utilized in any. gelatino-silver halide system to improve its efficiency. The invention is also very useful in the so-oalled graphic arts films, i.e., lithographic films. In all cases when one of the hydroxyalkyl vinyl ether polymers or copolymers is present in the amounts set forth above, ahigher density is obtained from a given amount of metallic silver in the developed photographic layer. Although the efiect is more noticeable in largegrain emulsions, it is also effective in small-grain emulsions.

The processes of the invention are quite simple, and consist of merely admixing with the molten or liquified emulsion after the digestion step, an aqueous solution of the hydroxyalkyl vinyl ether polymeric material. As an exemplary procedure, a gelatino-silver iodobromide emulsion is prepared by conventional methods. The silver halides are precipitated in gelatin and the resulting dispersion or emulsion ripened. The emulsion is then 3 washed, either after chilling and noodling, or after coagulation by decanting the supernatant liquid. The emulsion is then redispersed and then it is digested to bring it to maximum speed. Following digestion, the polymeric material (usually in aqueous solution) is added to the molten emulsion in an amount sufficient to provide the desired ratio of polymer to total solids. The usual final'additions, e.g., of hardener, antifogging agents, sensitizing agents and spreading agent, are made and the emulsion is coated on a suitable support and dried in the usual manner. To test the effectiveness of'the hydroxyalkyl vinyl ether polymers, the element is exposed in a 'sensitomete'r according to a procedure based on the American Standard Method for the S-ensitometer of Medical X-ray Films PI-I2.91956.

The sentitometer used in the following examples was equipped with a neutral density /2 step wedge. The density of a selected step, as set forth in the tables, was measured and the quantity of metallic silver per square decimeter was determined by analysis. The density divided by the quantity of silver ingrams per square de cimeter was taken as an expression of covering power.

The invention will now be further illustrated by, but is not intended to be'limited to the following examples. The quantities of hydroxyalkyl vinyl ether polymeric materials are given as a percentage of the weight of total solids in the emulsion.

Example I Fifty grams of polyvinyl alcohol which was substantially 100% hydrolyzed polyvinyl acetate and of which a 4% aqueous solution at 20 C. had a viscosity of 4-6 centipoises .was treated with one hundred grams of ethylene oxide in the manner described in the Cohen et al., J. Poly. Sci., 11, 193 (1953) reference noted above at 80 C. for 28 hours. The resulting product was added to a high speed g'elatino-silver iodobromide emulsion which was made in the usual manner and digested with an organic sulfur compound and gold chloride. The emulsion contained approximately 1.6 mole percent of silver iodide and 98.4 mole percent of silver bromide. The emulsion was divided into threeportions and to each of two portions there was added enough of the. polymeric material described above to give the percentages based on total solids in the emulsion shown in the table below. The remaining portion served as a control. The emulsions were coated and dried in the conventional man- ,ner. The coatings were exposed in the sensitometer and developed for 5 minutes in a developer of the composition:

Water to make 1000.0 ml.

Following development the films were fixed, washed and dried in the conventional manner. The results of the sensitometric tests and measurements of covering power are shown in the following table:

Covering Percent Maximum Power at Oopolymer Density density 1.6:lz0.1

Example 11 Example -I was repeated except that the polyvinyl al- 4 cohol was reacted at 60 C. for 64 hours. The resulting material was added to the silver iodobromide emulsion defined in Example I and coated and dried, exposed and processed as described therein with the following results:

Covering Percent Maximum Power at Polymer Density Density of Example III! In a ZOO-ml. polymer flask fitted with a stirrer, reflux condenser, thermometer and nitrogen inlet below the liquid surface were placed 50 grams of freshly distilled hydroxyethyl vinyl ether and 50 grams of freshly distilled t-butyl alcohol. The solution was heated to C. for 10 minutes while purging with nitrogen and 0.5 gram of azobisisobutyronitrile was added. The resulting solution was heated under nitrogen overnight or about 16 hours. The volatile materials were removed at reduced pressure on a steam bath. The resulting residue was redissolved in alcohol and again evaporated to dry- Finally, the polymer was dried for one hour at C. at 0.5 mm.

The resulting polymer was added in the amount set forth in the table below to the gelatino-silver iodobromide emulsion made as described in Example I. The emul sions were coated and dried in the conventional manner. After aging for two weeks, the coated films were exposed and processed'as described above. The following results were obtained:

In a 200-ml. polymer flask fitted as described in Example III, there was placed 25 grams of freshly distilled hydroxyethyl vinyl ether and 25 grams of freshly distilled vinyl acetate and 50 grams of freshly distilled t-butyl alcohol. The solution was heated to 80 C. for 10 minutes while purging with nitrogen and 0.5 gram of a20- bisisobutyronitrile added. The resulting mixture was heated at 80-85 C. under nitrogen overnight. The volatile materials were removed over a steam bath at reduced pressure. The copolymer was isolated by evaporation to dryness, dissolving again in alcohol and reevaporating to dryness for one hour at 100 C. at 0.5 mm.

The resulting copolymer was then hydrolyzed by dissolving in 400 ml. of methanol and 400 ml. of a freshly prepared stock solution containing 30 grams of sodium methoxide in 500 ml. was added. The solution was heated under reflux overnight under a nitrogen atmosphere and then cooled and diluted with methanol to 1000 ml. Theneutralization equivalent was used to calculate the composition ratio. The ratio of hydroxyethyl vinyl ether to vinyl alcohol was 3.3. The copolymer was isolated by neutralization of the reaction mixture with acetic acid and concentration on the steam bath at reduced pressure. The copolymer was precipitated from methanol by addition of acetone and dried.

The resulting copolymer was added in the form of a 10% aqueous solution to the gelatino-silver iodobromide emulsion described in Example I to give the amounts shown in the following table together with the sensitometric results of testing as described above:

In a ZOO-ml. polymer flask fitted as described in Example III, there were placed 50 grams of 1/1 ratio by weight of a mixture of freshly distilled hydroxyethyl vinyl ether monomer and vinyl acetate monomer and 50 grams of freshly distilled t 'butyl alcohol. The solution was heated to 80 C. for minuteswhile purging with nitrogen and 0.5 gram of azo bisisobutyronitrile added. The resulting solution was heated at 80-85 C. under nitrogen overnight. -The volatile materials were removed at reduced pressure on a steam bath. The resulting product was redissolved in alcohol and again evaporated to dryness. It was then hydrolyzed by reaction with sodium methoxide in methanol. The ratioof ether to alcohol determined from the saponification equivalent was 0.91.

A gelatino-silver iodobrornide was made as described in Example I and divided into two parts. One part was used as a control and to the second part there was added the above polymer in an amount as designated in the following table. The emulsions were coated, dried, exposed and tested as described in Example I with the following results:

Covering Power Percent Maximum at densities Copolyrner Density Example Vl Covering Percent Maximum Power at Copolymer Density Density of 1 (Control)- g 2 28 15 2112 37 Example VII Example IV was repeated except that the reaction 00- polymerization ratio of hydroxyethyl vinyl ether to vinyl acetate was 6.4 and gave a conversion of 45%.

The resulting copolymer was added to the gelatinosilver iodobromide emulsion described in Example I and gave the results shown in the following table:

Covering Percent Maximum Power at Copolymer Density Density of Example VIII' l Example IV was repeated, except that 3 4 grams o'fhY droxyethyl vinyl ether and 16 grams of vinyl acetate were used in the reaction mixture for copolymerization. All other conditions and emulsion addition and testing were as described in Example I and the following results were obtained:

Covering Percent Maximum Power at Copolymer Density Indicated Densities 1 (Control) 0 31. 5(1. 29) 2 8 1.80 42. 2(1. 25) 3."- 15 2.22 47. 8(1. 41) 4 23 1. 37 37. 5(1. 35)

Example IX Example IV was repeated except that 38 grams of freshly distilled hydroxyethyl vinyl ether and 12 grams of freshly distilled vinyl acetate were employed in the polymerization reaction. All other conditions of obtaining the polymer were as described in Example IV. Testing of the copolymer for covering power effective- Example IV was repeated using a mixture of 40 grams of hydroxyethyl vinyl ether and 1 0 grams of vinyl acetate in the copolymerizing reaction mixture. All other conditions of obtaining the copolymer were as described in Example IV. Testing it in the gelatino-silve-r halide emulsion described in Example I for covering power ef fectiveness was carried out as described in that example. The following results were obtained:

Covering Percent Maximum Power at Oopolymer Density Indicated Densities 1 (Control) 0 1. 29 31. 551. 29) 2 15 2.22 47.9 1.28) 3 23 2. 22 38. 7(1. 35)

Example X I Covering Percent Maximum Power at Copolymer Density Indicated Densities It has been found that the increased covering power of photographic emulsion layers is not limited to adding the above described polymers and copolymers to the gelatino-silver halide emulsion layer. It can be attained by incorporating the polymeric ether in a gelatin composition to be coated next-to a gelatino-silver halide emulsion layer, e.g., in a gelatin suhlayer, a separator or lightfiltering layer or in an antiabrasion layer. The amount of polymeric material so used can be based on the total gelatin in the contiguous layers. A layer essentially composed of gelatin and one or more of the polymeric ethers described above in an amount from to 50% by weight of the total Weight of the two contiguous layers can be used [dry basis].

As will be apparent from the above description, the invention is not limited to the specific quantities or ratios of monomers as. shown in the examples. The hydroxyethyl vinyl ether monomer and vinyl acetate monomer are, both commercially available. Polyvinyl alcohol ethylene oxideand propylene oxide also are commercially available.

The invention is not limited to photographic gelatinosilver halide emulsions of the silver iodobromidetype. The invention may be applied to other gelatino-silver halide emulsions, e.g. gelatino-silver bromo-chloride emulsions of the lithographic type. The invention is particularly efiicacious in photographic emulsions whose average grain size is relatively large. The emulsions may contain any of the well-known optical sensitizing dyes as well as non-optical sensitizers such as sulphur sensitizers, e.g., allyl isothiocyanate, allyl diethyl thiourea, phenyl isothiocyanate and sodium thiosulfate; the polyoxyalkylene ethers disclosed in Blake et al., US. Patent 2,400,532 and the polyglycols disclosed in Blake et al., US. Patent 2,423,549. Other non-optical sensitizers such as amines as taught by Stand et al., US. Patent 1,925,508 and metal salts as taught by Baldsiefen, US. Patent 2,540,085 and Baldsiefen et al., US. Patent 2,540,086 may also be used. Antifoggants, e.g., benzotriazole and triazaindenes can be used as well as the usual hardeners, i.e., chrome alum, formaldehyde, etc. The emulsions may be coated on any suitable support such as paper or films composed of cellulosic esters, e.g., cellulose triacetate, cellulose acetate/butyrate; superpolymers, e.g.,

polyvinyl chloride/Co vinyl acetate, polyvinyl 'acetals, e.g. formal and acetal; polystyrene; polyamides, e.g., polyhexamethylene adipamide, and polyesters, e.g. polyethylene tcrephthalate, polyethylene terephthalate/isophthalate and those polyesters obtainable by condensing terephthalic acid or dimethyl terephthalate with propylene glycol, diethylene glycol, tetramethylene glycol or cyclohexane-1,4-dimethanol (heXahydro-p-Xylene alcohol). The vinylidene chloride copolymer-coated oriented polyester films of Alles et al., US. Patent 2,627,088 and Alles, US. Patent 2,779,684 are especially suitable. 1

An advantage of the invention is that it provides a simple, dependable and etfective means for providing gelatino-silver halide photographic emulsions of enhanced covering power. The eificiency of the resulting developed silver is increased, that is, it can provide greater density per quantity of metallic silver which results from development.

Another advantage of the invention is that the addition of the hydroxya lkyl vinyl ether polymers and copolymers to photographic emulsions requires no special technique and can be carried out by the ordinary technician with conventional apparatus; Since the polymers and copolymers are water soluble they can be added from an aqueous solution and they do not provide the problems of solvent recovery. Also, the resulting modified gelatino-silver halide emulsions can be coated and dried in the conventional coating and drying apparatus which oflers obvious commercial advantages. Still further advantages will be apparent from the foregoing description of the invention.

What is claimed is:

1. A photographic silver halide emulsion comprising on a dry basis, by weight, 30% to 75% silver halide, 20% to gelatin and 5% to 50% of a Water-soluhle fi-hydroxyalkyl ether of a polyvinyl alcohol, wherein the alkyl group contains 2 to 3 carbon atoms, said ether containing intralinear units represented by the formulae -[CH CH (OR)] and [CH -CH(OH)] Where m and n represent the proportions of said units in the polymer and mm is in the ratio of 1:0 to 0.321.

2. An emulsion according to claim 1 wherein said ether is a fl-hydroxyethyl ether.

3. An emulsion according to claim l wherein said ether is a fl-hydroxypropyl ether.

4. An emulsion according to claim 1 wherein said ether is a hydrolyzed p-hydroxyethyl vinyl ether/vinyl acetate copolymer.

5. An emulsion according to claim 1 wherein said silver halide is silver iodobromide.

6. A photographic element comprising a support, a gelatino silver halide emulsion layer having in intimate association therewith a substantial quantity of a watersoluble li-hydroxyalkyl ether of a polyvinyl alcohol wherein the alkyl group contains 2 to 3 carbon atoms, said ether containing intralinear units represented by the formulae [Cl-I;,,-CH(OR)] and [CH -.-CH(OH)] Where m and n represent the proportions of said units in the polymer and mm is in the ratio of 1:0 to 0.3:1.

7. An element according to claim 6 wherein the emulsion layer contains 5% to 50% by Weight of said ether and a gelatin layer containing said ether in an amount constituting 5% to 50% by weight of the total Weight of said layers.

8. An element according to claim 6 wherein said ether is in said emulsion layer.

9. An element according to claim 8 wherein said ether is a B-hydroxyethyl ether.

10. An element according to claim 8 wherein said ether is a fi-hydroxypropyl ether.

References Cited in the file of this patent FOREIGN PATENTS 687,751 Great Britain Feb. 18, 1953 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION COMPRISING ON A DRY BASIS, BY WEIGHT, 30% TO 75% SILVER HALIDE, 20% TO 65% GELATIN AND 5% TO 50% OF A WATER-SOLUBLE B-HYDROXYALKYL ETHER OF A POLYVINYL ALCOHOL, WHEREIN THE ALKYL GROUP CONTAINING 2 TO 3 CARBON ATOMS, SAID ETHER CONTAINING INTRALINEAR UNITS REPRESENTED BY THE FORMULAE 